Electronic products used in daily lives continue to evolve due to advances in technology, for example, smaller and more powerful mobile phones are being developed that provide personalized global positioning and navigation functions, and therefore need a variety of sensors for condition detection. Currently, most of the magnetic field sensors utilizing magnetic field sensing principle are Hall sensors and biaxial anisotropic magneto-resistor G sensors (AMR G sensors), but these still have the issues of bulky volume, low sensitivity and etc. In addition, tunneling magneto-resistive sensors (TMR sensors) provide good sensitivity and small volume. The TMR sensors are only suitable for the production of single axial sensing rather than electronic compasses due to low sensing linearity.
Based on the shortcomings of the aforementioned various sensors, a complementary tunneling magneto-resistive structure has been proposed. Two TMR sensors are connected in parallel to complement each other, thereby resolving the issue of poor sensing linearity. In a TMR magnetic field sensor, in-plane magnetic anisotropy (IMA) materials are generally used as the magnetic layers in a magnetic tunneling junction (MTJ). A MTJ structure typically consists of a thin and non-magnetic dielectric layer and magnetic layers above and below the non-magnetic dielectric layer. A pinned layer, a tunneling layer and a free layer are also included. Signal output of the TMR magnetic field sensor is achieved by employing a single horizontal annealing field to set the magnetization direction of the X-Y axial fixing layer (as a reference layer), and detecting the direction of an externally-applied magnetic field by determining the changes in resistance caused by the difference between the magnetization direction of pinned layer and the magnetization direction of the free layer (as a sensing layer) modified by the externally-applied magnetic field. When there is no external magnetic field, the magnetization direction of the free layer remains in the lowest energy state, thus the initial state of the magnetization direction of the free layer can be controlled by crystalline anisotropy, the shape anisotropy, current field, demagnetization field, and etc.
Although the complementary tunneling magneto-resistive structure solves the problem of poor linearity in magnetic field sensing, it is the trend to improve the sensitivity and linearity of the complementary tunneling magneto-resistive structure.